A method measures the backlash at an axial joint of an industrial robot having a first and a second robot knuckle that are movably connected to each other in a direction of rotation by the axial joint. A load-transmitting device applies a predeterminable force alternately in a measuring line to the first robot knuckle, connected to the free end of a robot arm. A deflection sensor measures the deflection of the first robot knuckle at a predetermined distance from the axis of rotation of the axial joint, and an evaluation device connected to the displacement sensor calculates a turning angle of the first robot knuckle as a measure of a backlash present at the axial joint, taking into account the geometrical arrangement data in the measurement of the deflection sensor and the industrial robot and also the measured deflection.